High-voltage direct-current system



- R. E. HELLMUND. HIGH VOLTAGE DIRECT CURRENT SYSTEM.

APPLICATION FILED SEPT. 10. 19H.

1,396,839. Patented Nov. 15, 1921.

3 SHEETS-SHEET I.

MTNEs'sEsG) i I? d/ IZYE/NfTC/J; d I 010/ a man 2 4 W m ATTORNEY R. E.HELLMUND.

HIGH VOLTAGE DIRECT CURRENT SYSTEM.

APPLICATION FILED SEPT- 10, 1911.

1,396,839. Emma Nov. 15, 1921.

3 SHEETS-SHEET 2.

WITNESSES: 7 I INVENTOR 71.4,; 4Q fiw/fn/ /mm M ATTORNEY R. E. HELLMUND.

HIGH VOLTAGE DIRECT CURRENT SYSTEM.

APPLICATION FILED SEPT-10. 1917.

9 39 Patented Nov. 15, 1921.

3 SHEETS-SHEET INVENTOR WITNESSES:

BY M U ATTORNEY RUDOLF E. HELLMUND, OF SVJ'ISSVALE, PENNSYLVANIA,ASSIGNOR TO \VESTING- HOUSE ELECTRIC SYLVAN IA.

& MANUFACTURING COMPANY, A CORPORATION OF PENN- HIGH-VOLTAGEDIRECT-CURRENT SYSTEM.

Specification of Letters Patent.

Patented Nov. 15, 1921.

Application filed September 10, 1917. Serial No. 190,503.

To all whom it may concern:

Be it known that I, RUDoLr E. HELLMUND, a citizen of the German Empire,and a resident of Swissvale, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in High-VoltageDirect-Current Systems, of which the following is a specification.

My invention relates to high-voltage, direct-current systems, andparticularly to the inherent overload protection of powerstation orsubstation generators for supplying voltage to the operating circuits ofa hi h-voltage railway system.

Tn the operation of high-voltage, directcurrent railway systems; forexample, 3000- volt systems, considerable difiiculty has beenencountered in preventing station generators from flashing over, in theevent of short circuits upon the railway system. well known, the circuitbreakers commercia-lly available, although operating to open a circuitin a very small fraction of time, nevertheless permit the short-circuitcurrent to instantaneously rise to a dangerous value. Consequently,further protection, preferably of an inherent character, is desirable,if not necessary, for satisfactory operation of the station generators.

The object of my present invention, therefore, is to provide arelatively simple system of the above-indicated character, whereby theinstantaneous rise of short-circuit current is sufficiently delayed bythe inherent characteristics of the generator system to permit thecircuit-breaker to open the generator circuit before dangerously highcurrents are attained. 1

My invention may best be understood by reference to the accompanyingdrawings, wherein Figure 1 is a diagrammatic view of the componentelements, namely, station generating apparatus and railway rollingstock, of a high-voltage direct-current railway system embodying theinvention; Fig. 2 is a diagrammatic view of a modified form of generatorsystem constructed and arranged in'accordance with the invention; Fig. 3is a sequence chart of well-known form, indicating the preferred orderof operation of the switches that are shown in Fig. 2; Fig. 4 and Fig.5, Fig. 6 and Fig. 7, Fig. 8 and Fig. 9, are views, respectively corre-As is sponding to Fig. 2 and Fig. 3, of further modifications of myinvention.

eferring to Fig. l of the drawings, the system shown comprisessupply-circuit conductors Trolley and Ground; a power-sta- C1011. orsubstation direct-current generator having an armature A and an excitingfield winding F; a driving induction motor M for the direct-currentgenerator; an auxiliary exciter 5 that is also driven by the motor M atransformer 6 that is associated with the various machine circuits in amanner to be set forth; a variable resistor 7 for adjusting the excitingcircuits, and a railway vehicle 8 that operates in the customary manner,receiving energy from the trolley and returnmg it through the rails toground.

It will be understood that, in lieu of the driving induction motor M,any suitable type of prime mover, such as a steam turbine or agasolene-engine, may be employed, if desired.

The exciter 5 comprises a commutaton type armature 15, which is mountedupon the operating shaft 16 of the main motor generator set, and aseries-related field windlng 17.

The transformer 6 comprises a winding 18 having a relatively largenumber of turns and a second winding 19 having a smaller number ofturns, both of the windings being disposed, in any suitable manner, upona common core member 20.

s is customary station practice, a suitable circuit-breaker is connectedin series relation with the main generator armature A to interrupt thegenerator circuit under overload conditions. Since the particular typeof circuit-breaker that is employed is immaterial to my presentinvention, I have not deemed it necessary to illustrate anycircuit-breaker in detail, but have merely shown the trip-coil andcontact members, which are labeled Circuit breaker.

Under normal operating conditions, the main generator current, indicatedby the solid arrows, is established from the ground through transformerwinding 19, main armature A and the circuit-breaker trip-coil andcontact members to the trolley. The auxili ary exciting circuit,indicated by the dotted arrows, is established from the positiveterminal of the eXciter armature 15 through increased voltage dropobtains across thewinding 19.

- ing predominates, and,

armature current in the opposite direction to the current through theother transformer relatively large number of turns, this'windundernormal operating conditions, the transformer core 20 is highlysaturated, so that slight changes of generator current or slight voltagefluctuations produce a substantially negligible effect in thetransformer 6. The few-turn transformer winding 19, furthermore,inherently operates to generated for the following reasons. Upon anincipient rise of such current, a correspondingly transformer winding19, since both the main current and the exciting current-traverse thewinding in the same direction. Consequently,'a decreased voltage isavailable for delivery to the main field winding F from the exciterarmature 15, whereby'the mainarmature current is inherently caused tosubside to its average value. 'The converse action takes place in theevent of an incipient decrease of generated current, as will beunderstood. r

In addition, under short-circuit conditions uponthe railway system, orother conditions involving a. dangerously'heavy surge of generatorcurrent, the transformer 6 1nherently acts to delay the rise ofshort-circuit current until the station cicuit-breaker can open thegenerator circuit and thus eliminate the short-circuitconditions. i

The additional inherent transformer action just mentioned may beexplained as follows: upon the incipient rise of shortcircuit current,the total transformer flux is materially diminished by reason of thetraversal of the. main-generator current through the transformer winding19 differentially to the current in the normally predominating many-turnwinding 18, and a certain opposing vo tage is induced, under suchabnormal conditions, across the manyturn transformer winding 18. In thisway,"

by reason of the inherenttendency of the winding 19 to maintain itsformer energization, a material value of current is drawn from theauxiliary field winding 17 into the transformer winding 18, thusreducing the excitation of the main Since the winding 18 has a" maintaina substantially constant current lIl the'main armature A,

voltage; of the exciter and, therefore, the correspondingly decrease thevoltage of the main armature A. By reason of the nherent actionjustrec1ted, therefore, the rise of short-circuit current is sufficientlyretarded to permit thecircuit-brealrer to open the generator circuitbefore dangerously high currents are reached.

The normal starting operation of the illustrated motor-generator setrequires but a brief description; The induction motor M may be startedin any familiar manner to.

dr1ve the main armature Aand the exciter armature 15,'the voltage ofwhich rapidly builds up by reason of theillustrated closedcircuitconnections through the field-winding 17. The voltage of the mainarmature A may be varied by the station operator in any suitable manner;for example, by manipulating the illustrated resistor 7.

Referring'now to Fig. 2, the system shown comprises the supply-circuitconductors trolley and ground; the driving induction motor M and themain station generator with its related circuit breaker, as illustratedin 1; and, in addition, a motor-generator set 25 for exciting purposes;an auxiliary source of energy, such as a battery B; a plurality and R-2,for purposes field winding F to of variable resistors 3,111

to'be set forth; and;

a plurality of electrically controlled switches 1, 2, 3 and et.

The motor-generator set driving or motor coupled-b V 25 comprises aarmature 27, WillCll' is means of a shaft 28, for example,

to a generator'or exciting armature 29. V A' series-related fieldwinding: 30; a shuntfield winding 31, which may be varied through theagency of the resistor R2,; and a commutating and neutralizing. fieldwinding 32 are provided for the auxiliary driving armature27, while thegenerator armature29 has an exciting field winding 33 that is energizedin accordance with the load of the motor-generator set, and acommutatingfield windingBi, Under normal operating conditions, theenergization of the auxiliary field winding 33 in Fig. 2;-Fig. h Fig. 6"and Fig. 8'is sufiiciently great tohighly saturate the correspondingmagnetic circuit (not shown). Consequently, ordinary current or voltagefluctuations have practically no effect upon the flux corresponding tothe field winding 33, which is thusioperative for current-limitingpurposes only under abnormal overload conditions, as hereinafter fullyset forth.

The main generator armature A is connected, through. thecircuit-breaker, across the supply circuit, while the auxiliarygenerator armature 29.is connected, throughthe switch 3 andvariableresistor R, across the main field winding F. 'As previouslystated, the field winding 33 for the auxiliary generinherent regulation.

of the main armature ator armature'is connected in series relation withthe auxiliary-motor circuits, connection being completed to therespective supplycircuit conductors Trolley and Ground, through switch 1and variable resistor R1.

Assuming that the induction motor M is driving the main generator atnormal speed, and that it is desired to supply voltage to the trolleycircuit, the switches 2 and 4 are first closed, as indicated in step aof the sequence chart, Fig. 3, to connect the 'battery B through thevariable resistor R across the main-field winding F, and to initiallyshort-circuit the auxiliary field winding 30. By suitably adjusting there sistor R, the voltage of the main armature A may be increased to thedesired operating value.

Switch 1 may then be closed to start the motor-generator set, after thesupply-circuit voltage has thus been established, and, by suitableregulation of the resistors R1 and R2 and by auxiliary field winding 30in circuit, the voltage of the auxiliar generator armature 29 may beincreased to a value equivalent to quent energization of the maingenerator from the motor-generator set alone.

Assuming short-circuit conditions in the railway system after thegenerator system is normally operating, the voltage of the maingenerator A instantaneously decreases materially, in accordance withfamiliar principles, whereby the simultaneous voltage of the auxiliarydriving armature 27 is instantaneously held 'at a value greater thanthat of the supply-circuit voltage, which causes a rapid reduction ofthe current in that armature and in the series-related field winding 33for the auxiliary generator armature, by reason of the materiallydifferent-from-normal relation of the supplycircuit voltage and thecounter-electromotive force of the auxiliary driving armature. Theaction just recited is aidedby the damping eifect of the shunt fieldwinding 31 for the auxiliary driving motor. Since the speed of thearmature 27' is only slightly affected by changes of supply-circuitvoltage, by reason of such shunt excitation,

under the short-circuit conditions in question and the consequentinstantaneous drop of supplycircuit voltage, the damping effect of theshunt field winding 31 tends to maintain a relatively highcounter-electromotive force in the armature 27 to effect the desired Thevoltage of the auxiliary generator armature 29 is thus quicklydiminished to correspondingly reduce the excitation of the main-fieldwinding F. In this way, the generator voltage A is further decreased toretard the rise of short-circuit current and permit the circuit-breakerto open the generator circuit before dangerous current conditions havebeen attained.

eference may now be had to Fig. 4, wherein the system shown comprisessupplycircuit conductors and a main motor-generator set similar to thoseillustrated in Fig. 3, and, in addition, an auxiliary motor-generatorset 40, a battery B1 for exciting one of the field windings thereof,variable resistors R and R1, and an inductive device 41.

The auxiliary motor-generator set is driven by, or mechanically coupledto, the main set in any suitable manner, a belt drive 42 being indicatedfor the sake of simplicity and clearness. Under operating conditions,however, the auxiliary set functions electrically in a manner similar toa mechanically independent set.

Electrically, the motongenerator set 40, in general, is similar to thepreviouslydescribed set 25, the chief difference residing in theconnection of the battery B1 through the switch 1, across the fieldwinding 33 for the auxiliary generating armature 29, which ield windingis normally energized in ac cordance with the load-current of themotorgenerator set 40. Furthermore, a shunt-field winding 44- for theauxiliary driving armature 27 is connected through switch 3, to oneterminal of the commutating field winding 32 and through variableresistor R1, switch 2, and variable resistor R, to the lower terminal ofthe auxiliary motor armature. 7

By reason of connecting the battery B1 across the auxiliary fieldwinding 33, a materially smaller-capacity battery may be utilized thanis necessary in the system shown in Fig. 2, wherein the storage batteryis employed to energize the main-field winding F.

The inductive device l-l may be of any well-known type and is employedfor the customary purpose of limiting or choking down sudden variationsof current in the circuits wherein it is connected. lVhen traversed byboth the main-armature current and the exciting current, a doublecurrentlimiting function is performed by the inductive device, whichalso acts, in a similar manner to the transformer winding 19 of Fig. 1,to inherently prevent current changes. 7

In the present case, the main-armature circuit, indicated by the solidarrows, is established from the ground through the inductive device 41,the main armature A and the circuit-breaker to the trolley.

The exciting or main-field winding circuit, indicated by the dottedarrows, is established from the positive terminal of the generatorarmature 29, through the inductive device 41, main-field winding F andcommutating field winding 3 1, to the negative terminal of the generatorarmature 29. As indicated in the sequence chart, Fig. 5, switch 1 isinitially closed after the two motor-generator sets are operating atnormal-speed conditions, whereby the voltage .of the auxiliary generatorarn'iature 29 is quickly built up to the desired value in accordancewith the adjustment of the resistor R. V

The second step of the control involves the closure of switch 3toinclude the field windingdl for the auxiliary driving armature 27 incircuit. v

As soon as the exciting system conditions have become stable, the switch2 maybe closed and the switch 1 may be opened, as indicated in thesequence chart, to connect the motor armature 27 in circuit and todisconnect the battery B1 to effect the normal excitation of the maingenerator from the auxiliary motor-generator set alone.

The inherent operation of. the illustrated system to retard the rise ofshort-circuit current issubstantially identical with the op ration setforth in connection with Fig.

2, by reason of the connection of the field winding 33 for the auxiliarygenerator armature 29 in series relation with the aux iliary motorarmature 27. Consequently, no further exposition-of deemed necessary. vV 7 The system of Fig. odiffers from that shown in Fig. .1; chiefly inth entire omission of storage batteries, and also in the connection of ashunt field winding 46 for the auxiliary driving variable resistor R2across that armature and another variable resistor R1, and in theconnection of the variable resistor B through.

switch 1 across the entire auxiliary generating machine, comprisingarmature 29 and field windings 34: and 83.

By reference to the sequence chart, Fig. 7, itwill be seen running,whereby the voltage of the auxiliary generator armature 29 rapidlybuilds up by reason ofthe local exciting circuit including switch 1,variable resistor Rand field windings 33- and 3a. 7 1

In the second step of the control, switch 3 is closed to energize thevmain-field winding F. As soon as stable excitation conditions obtain inthe system, switch '2 may be next closed and switch l'may be opened, asindicated in step 0 of the sequence chart, to permit the fullauxiliary-motor current to traverse the field winding 33 for the gen-.

erator armature 29; further regulation, if necessary, being accomplishedby suitable manipulation of the resistors R1 and R2.

. Inasmuch as the inherent action of the exciter system, toprevent adangerous rise .of overload;ma n generator current,.is similar to thatset such inherent action is '9, sw tch 4 1s closed, afterthe ma nmotorarmature 27, through a that switch 1 is initially closed after themotor-generator sets are switch 1 may be'closed forth in connection withFig. 2, no further description of such operation is considerednecessary.

lnFig. 8, the shaft 16 of the main motorgenerator set carries, inaddition to the driving induction-motor rotor generator armature A, anauxiliary machine 50, which is employed for starting purposes, to be setforth. 7 l v 'An auxiliary motor-generator set 51, comprising.-armatures 27 and 29 andfield windings 33: and 4A, is utilized forseparately exciting the main-field winding F, variable resistors R1 andR2 being connected in series circuit relation with the auxiliary fieldwindings 33 andll, respectively. i

.The auxiliary machine 50 comprises a commutator-type armature 55, whichis driven by the induction motor M, andja field winding, 56, which isconnected throughswitch 4 and variable resistor R- across the supplycircuit. The induction device 41 and a fxed-resistjor 52 are connectedin seriescircuit relation with the auxiliary farmature .55, which maylikewise beconnectedto the'supply-circuit conductor Trolley by switch4;, theprovision of such impedance devices effectively preventingdangerous current conditions in the auxiliary armature 55, at any time.H

As indicated in-the sequence chart, Fig.

field winding 1 maybe increased to any deto establish a supsired valueby adjusting the resistors R1 HHCl RQ. 7 I i r l,

After stable excitation conditions obtain, to connect the main throughthe circuit breaker,to the a supply circuit, and, if desired, switch lmay then be'opened to allow the auxiliary machine 50 to run, idle, orthe machine 50 maybe utilized to supply a portion of theZne'cessaryenergy tothe highe generator armature A,

volta e railway s stem.

. As hereinbefore mentioned, the auxiliary machine 50 isprotectedagainst short-circuit conditions, through the agency of the impedancedevices {l1 and 52, while dangerous increases of main generator currentare again prevented through the previouslydescribed inherent action ofthe field winding 33 for the auxiliary generator armature .29, whichfield windingis connected in series relation with the auxiliary drivingmotor. V I do not wish to be restricted tot-he speand the maincificcircuit connections or arrangement of parts herein set forth, as variousfurther modifications thereof may be effected without departing from thespirit and scope of my invention. I desire, such limitations shall bedicated in therefore, that only imposed as are inthe appended claims.

I claim as my invention:

1. In a system of distribution, the combination with a direct-currentgenerator, of an auxiliary exciting system therefor, an inductive meansin said system for inherently counteracting overload generator currentsof large amplitude to a greater extent than upon smaller loadincrements.

2. In a system of distribution, the combination with a direct-currentgenerator, of an auxiliary exciting system therefor, and inductive meansinherently active only under predetermined abnormal conditions forretarding the rise of enerator current.

3. In a system of istribution, the combination with a maindirect-current generator, of an auxiliary generator for exciting themain generator, and means dependent upon the inherent action of theauxiliary generator circuits for retarding the rise of main-generatorcurrent under predetermined abnormal overload condition only.

4. In a system of distribution, the combination with a maindirect-current generator, of an auxiliary generator for exciting themain generator, and a motor for driving said auxiliary generator, saidauxiliary generator having a field winding energized in accordance withthe load current of said motor to normally produce magnetic saturationconditions.

In a system of distribution, the combination with a mam direct-currentgenerator, of an auxiliary generator for exciting the main generator, amotor for driving said auxiliary generator, said auxiliary generatorhaving a field winding energized in current of said magnetic saturaiorinitially enerfield winding.

accordance with the load motor to normally produce tion conditions, andmeans gizing the main generator In a system of distribution, thecombination with a main direct-current generator, of an auxiliarygenerator for exciting the main generator. a motor for driving saidauxiliary generator, said auxiliary generator having a field windingenergized in accordance with the load current of said motor to normallyproduce magnetic saturation conditions, and means for initiallyenergizing said auxiliary generator field winding.

7. In a system of distribution, the combination with a maindirect-current gen-erator, of an auxiliary generator for exciting themain generator, a motor for driving said auxiliary generator, saidauxiliary generator having a field winding energized in accordance withthe load current of said motor to normally produce magnetic-saturationconditions, and means for initially closing an auxiliary excitingcircuit around said auxiliary generator.

8. In a system of distribution, the combination with a load circuit, ofa main directcurrent generator, an auxiliary direct-current generator,and a driving motor for said auxiliary generator, the field winding ofsaid main generator being energized by said auxiliary generator, thefield winding of said auxiliary generator being energized from said loadcircuit in series circuit with said driving motor, and said seriescircuit be ing so designed that the magnetic flux of said auxiliarygenerator is only slightly affected by slight voltage fluctuations ofsaid load circuit but is materially decreased by an abnormal voltagedrop in said load circuit.

In testimony whereof, I have hereunto subscribed my name this 30th dayof August, 1917.

RUDOLF E. I-IELLMUN D.

